The present invention relates to a method and means for increasing the utilization (i.e., lifetime) of cathode sputtering targets. The invention has particular utility in magnetron sputtering of targets comprising costly components, e.g., as in the manufacture of magnetic and magneto-optical (xe2x80x9cMOxe2x80x9d) recording media comprising magnetic alloys including precious and/or rare metals.
Magnetic and MO recording media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disk form, such as utilized in computer-related applications, typically comprises a non-magnetic metal substrate, e.g., of an aluminum (Al)-based alloy such as aluminum-magnesium (Alxe2x80x94Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate surface, a plating layer, e.g., of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of carbon (C) or carbon doped with at least one of hydrogen (H), nitrogen (N), and fluorine (F).
According to conventional manufacturing methodology, a majority of the layers are deposited by cathode sputtering. A similar situation exists in the manufacture of magneto-optical (MO) media, in which a layer stack comprising a plurality of thin film layers, such as alloy layers having reflective properties or thermo-magnetic properties (e.g., TbFeCo, etc.) for functioning as writing, writing assist, and read-out layers, are sequentially sputter deposited on a suitable substrate surface.
The areal recording density (e.g., bits/in2) of magnetic data storage media has increased rapidly and significantly in recent years, and, to accommodate this rapid increase in areal density, both media performance and manufacturing cost have become extremely critical. Precious metal-containing sputtering targets, e.g., of Co-based magnetic alloys containing Pt, such as CoCrPt and CoCrPtB, are commonly utilized in the manufacture of magnetic recording media in order to provide the very high magnetic anisotropies required for obtaining the increased areal recording densities. A similar situation exists with MO recording media, wherein the thermo-magnetic layer(s) comprise rare elements such as Tb. However, due to the high cost of the precious or rare metals, e.g., Pt and Tb, sputtering targets comprising same are very costly. Further, when sputtering targets, particularly magnetically enhanced targets, e.g., magnetron targets, are utilized according to conventional practices, the target material usage is typically limited to 30-40 wt. % or less. Thus, the high purchase cost and low utilization of conventional sputtering targets disadvantageously result in increased manufacturing cost of magnetic and MO recording media.
Therefore, there exists a clear need for improved sputtering target means and methodology for increasing target utilization, particularly of precious metal-containing targets, to greater than about 40 wt. %, while maintaining good performance and film uniformity of the resultant thin-film magnetic or MO recording media.
The present invention addresses and solves the problems and drawbacks attendant upon the poor utilization of sputtering targets, such as planar magnetron sputtering targets comprising expensive precious metal components, while maintaining full compatibility with all aspects of conventional automated manufacturing technology for thin-film magnetic and MO recording media. Further, the methodology and means afforded by the present invention enjoy diverse utility in the manufacture of numerous and different devices requiring sputtered thin film layers and/or coatings, e.g., optical devices, architectural glass, semiconductor devices, protective and decorative coatings, etc.
An advantage of the present invention is an improved method for performing sputtering of a target, whereby utilization of the target material is significantly increased.
Another advantage of the present invention is an improved sputtering target providing significantly increased utilization of the target material.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a method of sputtering a target, comprising steps of:
(a) providing a magnetically enhanced sputtering apparatus comprising a sputtering target having a first, sputtering surface and a second, opposing surface facing and in electrical contact with a cathode of the sputtering apparatus;
(b) sputtering the first surface of the target to form a first erosion track therein;
(c) removing the target from the sputtering apparatus when the first erosion track reaches a predetermined depth below the first surface;
(d) reinstalling the sputtering target in the sputtering apparatus such that the second surface is the sputtering surface and the first surface is the opposing surface and faces and is in electrical contact with the cathode via an intervening backing plate, the backing plate being comprised of at least one material selected for causing a second erosion track to be formed in the second surface of the target during sputtering therefrom which is laterally displaced from the first erosion track; and
(e) sputtering the second surface of the target to form the laterally displaced second erosion track therein to a predetermined depth below the second surface, thereby increasing the utilization of the sputtering target.
According to preferred embodiments of the present invention, step (a) comprises providing a magnetron sputtering apparatus, e.g., a planar magnetron sputtering apparatus; and providing a sputtering target comprised of a material for forming a layer of a thin film magnetic or magneto-optical (MO) recording medium, e.g., comprised of a material selected from the group consisting of nonmagnetic metals or alloys, magnetic metals or alloys, dielectrics, thermo-magnetic alloys, and carbon or carbon compounds.
In accordance with preferred embodiments of the present invention, step (d) comprises providing a backing plate comprised of a material which affects (i.e., alters) passage of magnetic flux through the target; wherein the composition and thickness of the backing plate are selected for obtaining the desired laterally spaced second erosion track on the second surface of the sputtering target.
According to further preferred embodiments of the present invention, step (d) comprises providing a backing plate comprised of Cr or a CoCr alloy, e.g., wherein the Cr content ranges from 0 to about 100 at. %, and the thickness ranges from about 0.1 to about 1 inch.
Another aspect of the present invention is a sputtering target comprising:
opposing first and second major surfaces, the first surface including a first erosion track formed therein by sputtering therefrom in a magnetically enhanced sputtering apparatus; and
a backing plate mounted on the first surface, the backing plate being comprised of at least one material selected for causing a second erosion track to be formed in the second surface of the target during sputtering therefrom in the magnetically enhanced sputtering apparatus, the second erosion track being laterally displaced from the first erosion track.
According to preferred embodiments of the present invention, the sputtering target is comprised of a material for forming a layer of a thin film magnetic or magneto-optical (MO) recording medium, e.g., a material selected from the group consisting of non-magnetic metals or alloys, magnetic metals or alloys, dielectrics, thermo-magnetic alloys, and carbon or carbon compounds; and the backing plate is comprised of a material which alters passage of magnetic flux through the target, wherein the composition and thickness of the backing plate are selected for obtaining the laterally displaced second erosion track on the second surface of the sputtering target.
Preferred embodiments of the invention include those wherein the backing plate is comprised of Cr or a CoCr alloy, wherein the Cr content ranges from 0 to about 100 at. % and the backing plate has a thickness ranging from about 0.1 to about 1 inch.
Yet another aspect of the present invention is magnetically enhanced sputtering apparatus comprising the above-described improved sputtering target comprising a backing plate mounted the first target surface having a first erosion pattern formed therein, with the backing plate operatively connected to a cathode of the sputtering apparatus and the second target surface functioning as the sputtering surface, wherein the backing plate is comprised of at least one material selected for causing a second erosion track to be formed in the second surface of the target during sputtering therefrom, the second erosion track being laterally displaced from the first erosion track.
Still another aspect of the present invention is a method of sputtering a target, comprising steps of:
(a) sputtering a first side of the target to form a first erosion pattern therein; and
(b) sputtering a second side of the target to form a second erosion pattern therein, the second erosion pattern being offset from the first erosion pattern.